Re: [PATCH v29 23/32] x86/cet/shstk: Add user-mode shadow stack support

Borislav Petkov
2021-08-27T18:46:00Z

On Fri, Aug 27, 2021 at 11:37:34AM -0700, Yu, Yu-cheng wrote:
> Right now, the kernel does lazy restore, and it waits until right before a
> task goes back to ring-3 to restore xstates. If a task needs to write to
> any xstate registers before that (e.g. for signals), it restores the whole
> xstates first and clears TIF_NEED_FPU_LOAD, which will prevent xstates being
> restored again later.

shstk_setup() allocates a shadow stack for the task and puts its pointer
in MSR_IA32_PL3_SSP.

What does that have to do with a task having to write any xstate
registers?

--
Regards/Gruss,
Boris.